Abstract

An Al(III) metal–organic framework (MOF) called Al-MIL-53-N3 (1) was synthesized under solvothermal reaction conditions using Al(NO3)3·9H2O and H2BDC-N3 (H2BDC-N3 = 2-azido-1,4-benzenedicarboxylic acid) ligand in a DMF/water (DMF = N,N-dimethylformamide) mixture. Phase purity was checked by performing X-ray powder diffraction, infrared spectroscopy and thermogravimetric analysis. Thermogravimetric analysis suggests that 1 is highly stable up to 300 °C under air atmosphere. The activated 1 (called 1′) showed a very fast fluorescence response to H2S (turn-on) and Fe(III) ions (turn-off) in an aqueous medium with excellent sensitivity and selectivity even in the presence of other potentially intrusive analytes. In the presence of H2S, the conversion of the azide moiety to amine is responsible for the fluorescence turn-on properties. On the other hand, the partial replacement of framework Al(III) ions by Fe(III) can be assigned for the selective detection behavior to Fe(III) ions. The detection limits (90.47 nM for H2S and 0.03 μM for Fe(III) ions in water) of 1′ are lower than those of the formerly reported MOF type of fluorescent sensors. The 1′-loaded J774A.1 macrophage cells are healthy and respond to intracellular H2S to exhibit strong blue fluorescence, confirming its suitability to detect H2S inside the cells. In addition, 1′ can detect H2S in human blood plasma (HBP) and sulfide ions in real water samples. These features make 1′ a very promising candidate for the on-site sensing of Fe(III) ions and the detection of intracellular and extracellular H2S.

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